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A. Freund

Publications and source records attributed to A. Freund.

26 records · Page 2Linked to original sources
arXiv1999

Evolution kernels of skewed parton distributions: method and two-loop results

We present a formalism and explicit results for two-loop flavor singlet evolution kernels of skewed parton distributions in the minimal subtraction scheme. This approach avoids explicit multiloop calculations in QCD and is based on the known pattern of conformal symmetry breaking in this scheme as well as constraints arising from the graded algebra of the $\cN = 1$ super Yang-Mills theory. The conformal symmetry breaking part of the kernels is deduced from commutator relations between scale and special conformal anomalies while the symmetric piece is recovered from the next-to-leading order splitting functions and $\cN = 1$ supersymmetry relations.

hep-ph↗
arXiv1999

Reconstruction of non-forward evolution kernels

We develop a framework for the reconstruction of the non-forward kernels which govern the evolution of twist-two distribution amplitudes and off-forward parton distributions beyond leading order. It is based on the knowledge of the special conformal symmetry breaking part induced by the one-loop anomaly and conformal terms generated by forward next-to-leading order splitting functions, and thus avoids an explicit two-loop calculation. We demonstrate the formalism by applying it to the chiral odd and flavour singlet parity odd sectors.

hep-ph↗
arXiv1999

Single spin asymmetry in DVCS

In the following note, we will present an estimation of the single spin asymmetry in deeply virtual Compton scattering (DVCS) which directly allows one to test predictions of the ratio of the imaginary part of the amplitude in DIS to DVCS, as well as access the skewed parton distributions at small $x$ in the DGLAP region. We find it to be large for the HERA kinematics to be accessible in forthcoming runs with polarized electrons.

hep-ph↗
arXiv1999

Diffractive Exclusive Photon Production in DIS at HERA

We demonstrate that perturbative QCD allows one to calculate the absolute cross section of diffractive exclusive production of photons at large $Q^2$ at HERA, while the aligned jet model allows one to estimate the cross section for intermediate $Q^2 \sim 2 GeV^2$. Furthermore, we find that the imaginary part of the amplitude for the production of real photons is larger than the imaginary part of the corresponding DIS amplitude by about a factor of 2, leading to the prediction of a significant counting rate for the current generation of experiments at HERA. We also find a large azimuthal angle asymmetry in $ep$ scattering for HERA kinematics which allows one to directly measure the real part of the DVCS amplitude and hence the nondiagonal parton distributions.

hep-ph↗
arXiv1999

Deeply Virtual Compton Scattering at HERA - A Probe of Asymptotia

We demonstrate that the measurement of an azimuthal angle asymmetry in deeply virtual Compton scattering (DVCS) at HERA energies, is experimentally feasible and allows one to determine for the first time the ratio $η$, of the real to imaginary part of the DIS amplitude. We further show that such a measurement would discriminate between different scenarios of the energy dependence of $F_2(x,Q^2)$ at energies beyond those reachable at HERA.

hep-ph↗
arXiv1998

DVCS at HERA

We demonstrate that perturbative QCD allows one to calculate the absolute cross section of diffractive exclusive production of photons at large $Q^2$ at HERA, while the aligned jet model allows one to estimate the cross section for intermediate $Q^2 \sim 2 GeV^2$. Furthermore, we find that the imaginary part of the amplitude for the production of real photons is larger than the imaginary part of the corresponding DIS amplitude by a factor of about 2, leading to predictions of a significant counting rate for the current generation of experiments at HERA. We also find a large azimuthal angle asymmetry in $ep$ scattering for HERA kinematics which allows one to directly measure the real part of the DVCS amplitude and hence the nondiagonal parton distributions.

hep-ph↗
arXiv1998

Nondiagonal Parton Distributions in the Leading Logarithmic Approximation

In this paper we make predictions for nondiagonal parton distributions in a proton in the LLA. We calculate the DGLAP-type evolution kernels in the LLA, solve the nondiagonal GLAP evolution equations with a modified version of the CTEQ-package and comment on the range of applicability of the LLA in the asymmetric regime. We show that the nondiagonal gluon distribution $g(x_{1},x_{2},t,μ^2)$ can be well approximated at small $x$ by the conventional gluon density $xG(x,μ^2)$. Keywords: Hard Diffractive Scattering, Nondiagonal distributions, Evolution

hep-ph↗